1. Field of the Invention
The present invention relates to a projection display device for projecting an image on an imager onto a screen or the like, and in particular is preferably used for a projection display device which projects light onto a projection plane from an oblique direction at a large spread angle.
2. Description of the Related Art
A conventional projection display device (hereinafter referred to as “projector”) is configured to project light from an optical engine onto a screen by a projection optical system, as shown in FIG. 11 for example. In this case, image magnification is attained on the screen by leaving a longer distance between the projector and the screen. However, no person or object can be located in a space between the projector and the screen, which leads to a problem of the space being not useful.
This problem can be solved by shortening a throw distance from the projector, for example. To that end, however, it is necessary to increase a diameter of a projection lens and decrease a focus length (giving a larger curvature of a projection lens), thereby causing a problem in which a projection lens needs to be of a huge size.
Meanwhile, it is possible to increase a spread angle of light projected from the projection optical system by reflecting the light by an aspherical mirror. According to this method, light is projected onto a screen plane from an oblique direction as shown in FIGS. 12A and 12B, and thus the projected light is less prone to be interrupted by an obstacle or the like. In addition, an increase in a spread angle of projected light (hereinafter referred to as “angle widening” of projected light) can be achieved by an aspherical mirror, avoiding the projection lens from being huge in size unlike the aforementioned case. Angle widening is achieved with use of a relatively small aspherical mirror, which prevents upsizing of a projector and increase in cost.
The foregoing projector using oblique projection may have either of two configurations for displaying a vertically long image (portrait display type) and displaying a horizontally long image (landscape display type). FIGS. 13A and 13B illustrate usage patterns of these projectors placed on a desktop. Whether landscape display or portrait display is suitable depends on the shape of a desk surface and positioning of an audience and a projector. Accordingly, if positioning of the projector does not meet the display type with respect to positioning of an audience and the like, for example, there will arise a problem in that a portion of a projection image extends off the desk surface, and the like, as shown in FIG. 14A.
This problem can be resolved by processing a circuit to display the extending portion in black (hide the portion) so that the projected image falls within the desk surface, as shown in FIG. 14B for example. In this case, however, only some of pixels on the imager are used, which leads to deterioration in picture quality of the projected image.
The present invention has been devised to solve the foregoing problems and is intended to provide a projection display device that is capable of projecting an image onto a projection plane in a smooth and favorable manner, without being bound by a shape of a projection plane or positioning of an audience and a projector.